Design is inherently a response to the needs of an ever-changing society, but do we have the knowledge-building toolkit these challenges demand? From economies, to cities, to natural ecologies, we live in a world of nested and deeply interconnected complex systems. A new mode of scientific inquiry shows great promise for informing the way designers approach some of the most pressing problems confronting humanity. This talk identifies the deficiencies of scientific reductionism as it is currently applied through design research, introduces complexity theory, and explores the lessons of systems thinking in iterative design. It will present and expand on the concepts of leverage points, feedback loops, emergence, mental models, and more.